Electric infrared heater



Nov. 10, 1970 D. c. WALLACE 3,539,770

ELECTRIC INFRARED HEATER Filed NOV. 14, 1967 I4 PORCELAIN I3 2 COATING vREFLECTIVE PORCELAIN 2 COATING I NVENTOR.

DOB/VALD a. WALLACE Y Ma 804;, Queue 8 Jewel! ATTORNEYS United StatesPatent US. Cl. 219345 3 Claims ABSTRACT OF THE DISCLOSURE An enclosedelectric infrared heater having an electric resistance heating coil, areflector positioned above the coil and a porcelain infrared emitted panof large area below the coil. The emitter pan can be maintained at atemperature of 850 to 900 F. at which temperatures it has an emissivityof at least 0.86 and emits a major portion of its infrared radiation inthe 3.0 to 5.0 micron wavelength band. For some reason the process ofthe invention increases radiation output by more than percent ascompared to the radiation output of conventional electric infraredheaters. The invention preferably includes a separate cover above thecoil with the reflector mounted on said cover between the top of thecoil and the bottom of the cover and spaced therefrom to provide aninsulated air space.

DESCRIPTION OF THE INVENTION The present invention relates to electricinfrared heaters and more particularly to a novel type of electricheater which provides the highest percentage of its emissive output inthe 3.0 to 5.0 micron wavelength band and which is much more eflicientthan previously known electric infrared heaters.

Electric heaters must be designed for high efficiency because of thehigh cost of electricity. Heretofere, conventional electric infraredheaters have relied upon high temperature emitters operating attemperatures above 1500 F. at which temperatures the highest percentageof infrared radiation is in the 2 to 3 micron wavelength band. I havediscovered that the radiation output can be greatly increased, e.g.,increased 10 to percent, by use of a novel type of electric heaterhaving a reflector above the heating coil and a low temperature infraredemitter of large area below the coil which emits most of the radiationin the 3.0 to 5.0 micron wavelength band.

The electric heater of the present invention employs a resistanceheating coil which can be heated to a high temperature, a cover abovethe coil, an infrared emitter with a relatively large heating area,preferably 3 to 6 square feet, and a reflector either acting as a coveror carried by a cover and serving to reflect heat from the coil towardsaid emitter. The emitter has its surface portions formed of a material,such as dark porcelain, with an emissivity at 900 F. of at least 0.86 inthe 3.0 to 5.0 micron wavelength band and is preferably heated to atemperature of around 800 to 950 F.

An object of the present invention is to improve the efliciency ofelectric infrared heaters.

Another object of the invention is to provide a simple, inexpensive,durable, compact, electric, infrared heater with maximum heat output andminimum operational cost.

A still further object of the invention is to provide a simple,inexpensive, electric heater suitable for heating a patio or an outsidework area.

These and other objects, uses and advantages of the invention willbecome apparent from the following description and claims and from thedrawings in which:

FIG. 1 is a top view on a reduced scale with parts ice broken awayshowing one embodiment of an electric infrared heater constructedaccording to the present invention;

FIG. 2 is a vertical section taken on the line 2-2 of FIG. 1 and on alarger scale; and

FIG. 3 is a vertical section similar to FIG. 2 showing a modified formof infrared heater constructed according to the invention.

Referring more particularly to the drawings, in which like parts areidentified by the same numerals througout the several views, FIGS. 1 and2 show one form of radiant heater A constructed according to the presentinvention having a bowl-like metal cover 1, an infrared emitter pan 2, aresistance heating coil 3, a sealed junction box 4, and a reflectivesurface 5 on the interior of the cover to reflect the heat to theemitter pan.

The cover 1 and the emitter pan 2 have marginal flanges 7 and 8 mountedon an anular asbestos gasket 9. The circular holes 10 of the gasket 9are aligned with the holes 11 of the annular flanges 7 and 8 to receivea series of bolts 12, whereby the cover may be rigidly connected to thepan with the gasket sandwiched between the flanges.

As herein shown, the pan 2 has a flat horizontal bottom surface 13 androunded sidewall portions 14. The cover 1 is preferably similarly shapedand has a flat upper surface 15 parallel to the surface 13. Insulatingmeans are preferably provided between the reflective surface 5 and thejunction box 4 to protect the wiring. As herein shown, a circularinsulator 16 is mounted in the central circular hole of the covercoaxial with the annular marginal flange 17 of the junction box which isattached by the bolts 28 to the cover 1. The electrical supply for theresistance element 3 extends through the electrical conduit 18 to thebox 4 and includes a plurality of insulated wires, such as 19 and 20,having connectors 21 and 22 connected to the vertical portions 23 of thecoil 3. The supply is usually 208 to 240 volts, alternating current.

As shown in the drawings, the heating coil 3 is in the form of aconcentric resistance element having straight radial horizontal portions24 extending outwardly from the unheated vertical portions 23 to theportions 25, which form the interior circle of the coil. A pair ofrounded end portions 26 connect the portions 25 to the circular outerportion 27 which forms the outer circle of the coil. Flat coils of thistype are well known in the art. While the coil shown herein has only twoconcentric circles, it will be understood that a similar coil having 3or more circles would also provide excellent results.

The upper and lower surfaces of the infrared emitter 2 must each have anarea of at least one square foot and must be formed of a material whichhas an emissivity and absorptivity of at least 0.86 at 900 F. and whichat that temperature will emit a major portion of its infrared radiationin the desired 3.0 to 5.0 micron Wavelength band. Such material ispreferably a glazed porcelain or the like with an emissivity andabsorptivity of at least 0.9 at 900 F.

If desired, the sealed enclosure formed by the cover pan 1 and theemitter pan 2 may be partially evacuated and maintained at asubatrnospheric pressure to minimize heat transfer by convection. Alsothe sealed enclosure may be filled with an inert gas, such as nitrogenor argon, or a gas with low heat conductivity.

A preferred form of infrared heater for carrying out the above processis shown in FIG. 3. This heater A is almost the same as the heater Apreviously described, but the reflector cover is replaced by a deepercover 111 having a reflector 50 mounted thereon as a separate element.The cover 1a is an inverted pan with a shape similar to that of theemitter pan 2. The sidewalls 30 of the cover 1a are generally similar tothe sidewalls of the cover 1 and have an annular flange 7a similar tothe flange 7, but they can have a greater axial height to accommodatethe reflector 50 and to provide an insulating air space between thereflector 50 and the cover 1a.

Like the cover 1, the cover 1a has a flat top wall 31 which may besuspended by pipe hangers 51 or the like from a ceiling or overheadsupport. As herein shown, these hangers are extended to provide verticalsupporting portions 32.

The reflector 50 is rigidly mounted on the cover 1 or the pan 2 in anysuitable manner. When the flange 7a is vertically spaced from the marginof the reflector, it is preferable to support the reflector from thecover. As herein shown, such support is provided by the portions 32which are internally threaded to receive the attaching screws 33. Thesehold the circular reflector coaxial with the pan 2 and the coil 3 andparallel to the coil and the flat walls 13 and 31. The margin of thereflector is preferably located at the marginal wall or the marginalflange of the heater to provide a closed air space above the reflector.

The reflector 50 has a reflective surface 5a similar to the surface 5and is spaced at least one inch from the top wall 31 to provide aninsulating air space 35 above the reflector and to reduce thetemperature of the cover. The reflector is covered by a layer 16B of asuitable heat insulating material such as fiber glass wool or Pyrowool.The thickness of the insulating layers is preferably at least one-halfinch or so. The unheated vertical portions 23 of the coil extend throughthe insulator 16A and are rigidly connected to and supported on thereflector 50 by insulated connectors 34.

The construction and location of the infrared emitter pan 2 are criticalin the practice of this invention. The bottom surface of the emitter 2should be heated to a temperature of 700 F. to 1000" F. when the heatingcoil 3 is maintained at a temperature of 1400" F. to 1600 F. Bestresults are obtained when the bottom surface of the emitter is at atemperature of 800 F. to 950 F. The upper surface of the emitter pan isheated by radiation and preferably has an absorptivity of at least about0.9 at 900 F. The lower surface of said pan must have an emissivity(i.e., total hemispherical emissivity) of at least 0.86 at 900 F. andpreferably has an emissivity of at least about 0.9 at 900 F. Such lowersurface must emit a major portion of its infrared radiation in the 3.0to 5.0 micron wavelength band and is preferably formed of a non-metallicheat resistant material with a high emissivity such as a porcelain orthe like. The preferred emitter pan comprises a sheet metal, such asaluminum, steel,

etc., with a thickness of one-eighth inch or less coated on both sideswith a dark colored porcelain having a high emissivity.

The emitter pan 2 must have a bottom surface with a relatively largesurface area of at least one square foot and preferably has a surfacearea of 3 to 6 square feet. The bottom wall of the emitter pan may behemispherical but is preferably generally flat for use with a flatheating coil. Such pan usually has a depth of 1 inch to 3 inches and awidth or diameter of to 40 inches, preferably 24 to 32 inches. Althoughthe pan 2 usually has a flat bottom surface 13 and rounded sidewallportions 14, as illustrated, the pan design can be varied by theintroduction of decorative patterns. The configuration can also bevaried to approximate more closely the shape of a saucer, bowl or even ahemisphere or, alternatively, can include some inverted curves so longas the pan configuration does not interfere with its installation.Similar changes in the design and configuration of the cover 1 arepossible, especially when a separate reflector 50 is employed.

The cover 1a is preferably shaped like the pan 2 and usually has aheight of 1 inch to 5 inches. It is usually formed of sheet metal, suchas aluminum or steel, and may be painted or plated. The cover preferablyhas thin walls with a thickness less than A: inch and preferably israther light in weight. The cover fits on the emitter pan to provide asealed container or enclosure with a height of 3 to 8 inches. Suchcontainer preferably has a width or diameter 3 to 8 times such height.

In order to reduce heat loss through the cover, it is desirable tominimize its temperature as by employing inslating means such as 16B oran air space between the reflector 50 and the cover. The heat transferto the cover can also be reduced by providing it with an inner surfaceof low absorptivity or by providing it with a polished or reflectivesurface. As herein shown, the cover 1a has a reflective surface 5bsimilar to the surface 5. Such reflective surface preferably has an areaof 3 to 6 square feet and may have various shapes but is preferablygenerally flat.

The reflector 50 may have a small curvature but is preferably generallyflat or generally parallel to the coil 3. Its peripheral edges arelocated radially outward of the margin of the coil and withinone-quarter inch of the marginal wall 30 of the cover or the marginalflange 8 of the emitter pan. The bottom reflective surface 5a of thereflector 50 preferably has a mirror-like finish and may be chromeplated or highly polished. The characteristics of the upper surface ofthe reflector 50 are not critical. The reflector may be made of a thinsheet metal or foil and may be made of aluminum or various other metals.

The reflector 50 is preferably spaced 2 to 4 inches from the top wall 31of the cover to provide at least one insulating air space above thereflector to minimize the heat transfer to the cover. Of course, suchheat transfer can be further reduced by partitioning the air space withaluminunr foil or additional reflectors similar to the reflector 50, butthis is not essential. If desired, the sealed enclosure formed by thecover pan 1 and the emitter pan 2 may be partially evacuated or filledwith an inert gas or a gas with a low heat conductivity as previouslystated.

In the heater of this invention the heating coil is preferably the solesource of heat nad may be of conventional construction so as to emit themajor portion of the infrared radiation in the 2 to 3 micron wavelengthband. The electrical apparatus should be capable of heating the coil toa temperature of 1400 F. .to 1650 F. or a temperature sufficient toprovide the desired emitter temperature at the bottom surface 13. Thecoil temperature should be maintained at 1400 to 1600 F. to provide thesurface 13 with a temperature of about 800 F. to about 950 F.

The shape of the heating coil 3 may vary considerably but such coil ispreferably generally parallel to the bottom wall of the infrared emitter2. The coil and said bottom wall are preferably generally flat. Thewidth or diameter of the coil is generally in the range of 1 to 3 feetand is usually 2 to 4 inches less than the internal dimension ordiameter of the flange 8 so that the periphery of the coil is disposed 1inch to 2 inches from the margin of the emitter 2. Such coil diameter orwidth is preferably 20 to 30 inches in most commercial heaters madeaccording to this invention. The thickness of the individual turns ofthe heating coil may vary but is usually around 0.3 to 0.6 inch.

In an electric heater of the type shown in FIG. 3 the coil 3 is spacedabout 1 inch to about 1 /2 inches from the reflector 50 and about 1 inchto about 1 /2 inches from the bottom wall of the emitter 2. The bottomsurface 13 is preferably maintained at a temperature of about 850 F. toabout 900 F. For example, in a typical commercial electric heater thecover 1a may have a diameter of 31 inches and a height of 4 inches, theemitter pan 2 may have a diameter of 31 inches and a height of 2 inches,the coil 3 may have a diameter of 28 inches and a thickness of one-halfinch, the insulating layer 16B may have a thickness of one-half inch,and the reflector 50 may have a diameter of 29 inches. In such heaterthe upper surface of the coil 3 may be spaced a distance of about 1%inches from the reflector 50 and its lower surface may be spaced thesame distance from the bottom wall of the emitter panZ so that the lowersurface of the pan is heated to a temperature of about 900 F. The uppersurface of he pan would, of course, be at a substantially highertemperature. In such a heater the sheet metal pan 2 is preferably coatedon both sides with a commercial glazed porcelain of dark color and highemissivity such as conventional A-19 porcelain. The exterior surface ofthe cover 1 may also be coated with porcelain or other heat resistant orcorrosion resistant material, but this is not essential.

A typical heater made according to this invention having a rating of6000 watts and a bottom surface temperature of 900 F. and suspended 8 to16 feet above the surfaces to be heated can distribute the infraredenergy to the solid objects below over a large area (i.e., up to adiameter of around 18 feet).

While the coil, pan and reflector, either with or without a separatecover, are designed in a planar circular form as depicted herein, theentire configuration of the heater can be changed with some resultantvariation in the efliciency of the system. For example, the plan asshown in FIG. 1 can be changed to an oval, elliptical, square,rectangular, rhomboid, triangular or other shape. Similarly, thevertical section can be changed to assume a circular, rectilinear orother shape.

It will be understood that, in accordance with the provisions of thepatent laws, variations and modifications of the specific methods anddevices disclosed herein may be made without departing from the spiritof the in vention.

Having described my invention, I claim:

1. An electric infrared space heater of exceptionally high efliciencycomprising a substantially planar wide resistance heating coil, aninfrared emitter below said coil comprising a round metal pan having amarginal portion radially outward of the periphery of said coil, saidcoil being spaced about one inch to about one and one half inches fromthe bottom of said emitter pan, said emitter pan having upper and lowersurfaces covered with a porcelain having an emissivity of at least about0.9 at 900 F., a cover above said coil and said pan comprising a roundinverted pan having a marginal portion rigidly secured to the marginalportion of said emitter pan, said emitter pan and said cover providing aclosed sealed oblate receptacle with a diameter of 1 to 3 feet, saidheating coil being supported by said cover in a horizontal positiongenerally parallel to the bottom of the emitter pan and having adiameter of at least one foot so that the periphery is closely spacedfrom the marginal portions of said pans, reflector means carried by saidcover above and spaced from said heating coil for reflecting heat fromthe coil downwardly toward said emitter, said reflector means extendingradially outward beyond the periphery of said coil, means for supplyingan electric current to said heating coil for maintaining said coil at atemperature of at least 1400 F. and sufficient to heat the lower surfaceof said emitter pan to a temperature of 800 F. to 950 F., said lowersurface having an area of at least 3 square feet and emitting the majorportion of the radiation therefrom in the 3.0 to 5.0 micron wavelengthband.

2. A high output infrared heater as defined in claim 1 wherein saidsealed receptacle has a diameter of about 24 to about 32 inches and aheight of about 3 to 8 inches and wherein said coil is circular and hasa diameter of about 20 to 30 inches.

3. A high output electric infrared heater as defined in claim 1 whereinthe marginal portion of said emitter pan comprises a radial marginalflange, said pan having a bottom surface with an area of about 3 to 6square feet, the marginal portion of said cover comprises a radialmarginal flange mounted on the flange of said emitter pan, the outerportions of the heating coil are spaced about one inch to about twoinches radially inward from the marginal flanges, and said reflectormeans is mounted on said cover about one inch to about one and one halfinches above the heating coil, said reflector means being spaced atleast about two inches from the top wall of the cover to provide atleast one insulating air space above the reflector means.

References Cited UNITED STATES PATENTS 1,954,128 4/1934 Heyroth et al.219-461 3,275,874 9/1966 Jennings. 3,345,498 10/1967 Siegla. 1,855,5074/1932 Bathrick 219-461 2,196,484 4/ 1940 Wentworth 219-461 X FOREIGNPATENTS 485,104 5/1938 Great Britain. 864,559 4/1961 Great Britain.

20,742 10/ 1935 Australia. 638,250 3/1962 Canada.

OTHER REFERENCES Westinghouse Engineer Pamphlet, Control of Radiant Heatby Surface Finish, by R. M. Leedy, July 1954, pp. 147-151.

Popular Science Pamphlet, Porcelain Panel That Heats a House, by MartinMann, March 1958, pp. 121- 123.

ANTHONY BARTIS, Primary Examiner U.S. C1.X.R. 219-342, 347, 354, 461,534, 553

